The present invention relates to a valve element as defined in the preamble of claim 1, comprising a main body, at least one inlet and at least one outlet, a passage connecting the inlet and outlet, at least one burst disk (rupture disk) or equivalent, which, when unbroken, closes the passage from the inlet to the outlet, and piston element comprising a piercing element or the like for piercing the burst disk.
A device corresponding to the subject of the invention is known from specification DE 2635076 A. One of the drawbacks of this solution is that the piercing element is returned by the action of pressure back to its original position, so a piece of the burst disk that may have been detached from it by the piercing action may partially block the passage and thus form an obstacle to the flow of pressure medium. In addition, the piercing element has to go completely through the burst disk in order to produce a hole of the desired size in the disk. If the piercing movement is for some reason incompletely executed, it will not produce a hole of the desired size.
The object of the present invention is to achieve a completely new type of solution that makes it possible to avoid the drawbacks of prior-art devices. The object of the invention is to create a reliable apparatus that can be utilized especially in fire extinguishing applications.
The apparatus of the invention is characterized in that the piston element is provided with a passage for a pressure medium, said passage extending axially through the piston element from one first side to one second side, that the piston element is provided with a second burst disk or equivalent, which, while unbroken, closes the passage provided in the piston element.
The apparatus of the invention is additionally characterized by what is stated in claims 2–7.
The solution of the invention has numerous significant advantages. The passage through the piston ensures that, after the second burst disk provided in the piston element has been pierced, the piston will be effectively pressed towards the first burst disk. The solution of the invention is leak-proof and reliable. By using a smaller second burst disk, it is possible to avoid the use of large actuators requiring a great power for the triggering action. By using an intermediate piece, such as a ball, reliable piercing of the second burst disk is achieved and additionally a situation is avoided where the piston of the actuator remains in contact with the second burst disk and no sufficient hole is produced in the burst disk. By employing two-stage triggering of the valve element, such that, during the first stage, the piercing of the second burst disk produces a flow of pressure medium into the cylindrical chamber, thereby causing the piston-piercer combination to move vigorously towards the first burst disk and pierce it, reliable operation of the valve element is achieved, ensuring that the passage from inlet to outlet is reliably opened. The valve element of the invention is thus excellently suited for use in fire extinguishing systems.